1 Paleoceanography Lecture 13 Coral evidence for temperature, salinity, and nutrient changes I. Corals as sub-annual resolution paleoceanographic archives spanning (at least) hundreds of thousands of years: a brief history A. 1972: Buddemeier and coworkers: used autoradiographs (bomb fallout) of Eniwetok corals to establish that x-ray visible density growth bands were annual in nature (at least at that site). Weber and Woodhead established O18-T relationship (offset in "light" direction from equilibrium) for some corals. Image removed due to copyright considerations. Sources: G.T. Shen. 2 Image removed due to copyright considerations. Source: Fairbanks and Matthews, 1978 adapted from Weber and Woodhead, 1972. 3 B. 1973: Weber shows inverse correlation between coralline Sr/Ca and temperature. Image removed due to copyright considerations. Source: Smith et al. (1979). C. 1974: Moore and coworkers: used other 228Ra/226Ra to date corals from other islands. In time, Moore and other workers would extend these radioisotope methods to other radioisotopes, such as 90Sr, 14C/12C, 210Pb... 4 D. 1977: Shackleton and Matthews do first study of 18O in Barbados high stand terraces. Image removed due to copyright considerations. D. 1978: Emiliani establishes annual cyclicity of coral 18O. Nozaki and Turekian present a 200 year record of 14C/12C: evidence for history of bomb 14C and initial explorations of 13C/12C as a tracer. Druffel and coworkers report other bomb 14C histories. Fairbanks and Matthews examine 18O from old (on-land) drilled coral terraces. E. 1979: Fairbanks and Dodge examine annual cycles of 18O and 13C in corals. 18O seems to go with T, but 13C may reflect light intensity (or growth rate, or some other correlated parameter). F. 1980's: lots of work on O18, C13, 90Sr, 14C, 210Pb. Shen begins first work on trace elements in corals (Pb, Cd). G. 1989: McConnaughey shows that portions of a contiguous annual band of a coral can show significantly different δ18O and δ13C, depending on orientation of band relative to sunlight. 5 Image removed due to copyright considerations. Source: McConnaughey, 1989. 6 Adkins modified McConnaughey calcification model: Image removed due to copyright considerations. Source: Adkins et al. (2003) GCA, figure 7. G. 1990's: the era of global change and the quest for understanding of decadal-century scale climate processes and variability. Image removed due to copyright considerations. Source: Cole et al., 1993. 7 Image removed due to copyright considerations. Source: Dunbar et al. (1994). H. 1992: Edwards and coworkers and Shen and coworkers begin the use of high precision TIMS Sr/Ca measurements as a temperature tracer. 8 Image removed due to copyright considerations. 9 Image removed due to copyright considerations. Source: deVilliers et al. (1995). I. 1993: groups of Edwards and Shen report that U/Ca is also temperature-dependent (even more so than Sr). 10 J. 1994: Fairbanks and coworkers report coherent 18O and Sr/Ca data from 18K Barbados corals suggesting >5°C temperature change during last glacial maximum. Image removed due to copyright considerations. Source: Guilderson et al. (1995). 11 K. El Nino in fossil 124 kyrBP Indonesian coral? – oxygen isotopes and Sr/Ca in a fossil coral that grew 124,000 years ago in Indonesia “reflect interannual variability in precipitation and sea surface temperature (SST) due to El Niño/Southern Oscillation (ENSO).” Image removed due to copyright considerations. Source: Hughen et al., 1999, figure 2. II. Deep Sea Corals Deep-sea corals grow for 50-200 years as solitary individuals attached to a hard surface (sometimes “mounds” of these occur growing on top of each other). Optical density banding is observed and the number of bands is approximately equal to the age of the coral (Cheng et al., 2000; but it is uncertain whether these bands are always annual, and it is not clear how to sample the coral to bring out temporal signals apart from moving from the attachment end towards the growth edge. Smith et al. (1997) pointed out that deep sea corals could be used to tackle paleo problems. Adkins et al. (1998) showed that 230Th/U, 14C, and Cd/Ca could be used to demonstrate decadal-scale changes in deep water properties in the deep Atlantic. 12 Image removed due to copyright considerations. Source: Adkins et al. (1998).